Microphotographic objective lenses must have high resolution and maximum contrast with minimum aberrations to provide acceptable results. When the desirable light path requires the use of a mirror, the objective lens must have a long back focal distance. To accomplish these objectives the prior art lenses have used many negative lens elements which has resulted in the distortion of the lens being large and the color correction at the 70 percent field of view becoming a problem.
According to the present invention there is provided an objective lens which has less than one percent distortion with a long back focal distance, wide angle coverage, high resolution and excellent color correction. The lens comprises from front to rear a double-plano filter, a negative meniscus lens element, a second negative meniscus lens element, a cemented doublet consisting of a biconvex lens element and a biconcave lens element, a second cemented doublet consisting of a biconcave lens element and a positive meniscus lens element, a third cemented doublet consisting of two planoconvex lens elements, a negative meniscus lens element and a double-plano protective cover plate.